armstrong-campbell-architects

Working With an Architect: Complete RIBA Plan of Work Stages Explained

Tue, 10 Feb 2026 00:26:26 GMT

Working with an Architect: The Complete RIBA Process Explained

So you've decided to hire an architect for your London house extension or new build project. This is a great first step but what happens next? What's the process? How involved will you be? What will you receive at each stage?

This guide walks you through the complete architectural process using the RIBA Plan of Work—the industry-standard framework that ensures your project progresses smoothly from initial ideas to finished home.

At Armstrong Campbell Architects, Leytonstone, we follow these stages for every project of any scale. The RIBA Plan of Work is a proven method that brings clarity to the complexity of delivering projects, ensuring nothing gets missed, and everyone is brought along the same journey.

The RIBA Plan of Work, Our Simplified Overview

The RIBA Plan of Work organises the process of briefing, designing, constructing and operating building projects into eight stages. For residential extension or new build projects, this framework provides structure to the design process and coordinates the work of the design team, consultants, and contractors. The framework has been refined over nearly six decades of architectural practice and represents the condensed learnings of the profession.

Each distinct stage has a defined outcome and decision points. Understanding these stages helps both architects and clients know what to expect, when key decisions need to be made, and how the project will develop.

The framework is procurement-neutral, meaning it works equally well whether you're using traditional procurement, design and build, or other arrangements. However, the procurement method you choose will affect how certain stages overlap and how design responsibilities are divided.

0- Strategic Definition

Pre-appointment of an architect, this is a project's initial feasibility process for a client, asking if it is right to progress with a project.

1 - Preparation and Brief

Define the project scope, deliverables and programme.

2. Concept Design

To establish the basic volumes and layout of the house, along with initial ideas for its internal and external appearance.

3. Spatial Coordination

To complete the overall look and feel of the project with sufficient detail that technical design can commence.

4. Technical Design

Refinement of the design and delivery of a full package of information such that a contractor can be appointed with an accurate design, cost and programme.

5. Construction

Both off-site manufacturing and on-site construction of the project.

6. Handover

Concludes the Building Contract and rectification of any defects.

7. In Use

Ongoing maintenance and review of how the building functions in real terms.

Stage 0: Strategic Definition

Stage 0 determines whether a building project is the appropriate means of achieving your objectives. For residential extensions, this stage typically involves assessing whether extending is preferable to moving, establishing budget parameters, and identifying major constraints.

The core tasks at this stage include developing client requirements, preparing a business case for feasible options, and reviewing project risks. The RIBA guidance notes that no design team is required for Stages 0 and 1—client advisers may be appointed to provide strategic advice before Stage 2 commences.

For many domestic projects, this stage is informal and can often be part of an initial site visit with the architect, often before they are appointed. It establishes the foundation for what follows. The outcomes include clarity about project objectives, rough budget parameters, and an initial assessment of feasibility. Usually a Fee Proposal and Architect’s Appointment will follow this.

Stage 1: Preparation and Briefing

Stage 1 develops the project brief, including project outcomes, sustainability outcomes, quality aspirations, and spatial requirements. This is the stage where the design team is typically appointed and where architect and client begin working together.

Core tasks include preparing the project Initial Brief, undertaking site appraisals, and assembling the project team. For residential projects, this involves commissioning measured surveys, researching planning constraints, reviewing Building Control records, and appointing structural engineers or other consultants as required. Consultants may be appointed at later stages.

The project brief should document spatial requirements, along with functional relationships, performance requirements, and aesthetic direction if given. The RIBA guidance emphasises that the brief should be sufficiently detailed to allow design to proceed without constant iteration. A well-developed brief at this stage prevents revisions later.

At the end of Stage 1, the Project Strategies should be established. These might include strategies for sustainability, planning, cost, health and safety, and procurement. These strategies provide a framework for coordinating specialist inputs throughout the design process.

Overall by the end of Stage 1, the project should be set up for the architect and client to begin designing.

We begin all projects with an Initial Programme as part of Stage 01 Preparation and Brief. The below is an example programme of a residential house in London and an overview note of what happens at each stage, prior to a detailed look in the following chapters.

An example of an early stage hand sketched plan, visually describing the conceptual approach to space planning with coloured backgrounds and indicative furniture.

Stage 2: Concept Design

Stage 2 develops and reviews initial design concepts based on the project brief. The architectural concept is prepared, and structural concepts are developed with the engineering team. This is where ideas take shape, where possibilities are explored, where the project begins to have form.

The RIBA guidance advises patience at this stage. While planning pre-application advice may be obtained, only experienced clients should consider submitting planning applications at Stage 2. The framework recommends that design concepts be properly tested and client sign-off obtained before proceeding to spatial coordination.

For residential extensions, concept design typically involves exploring alternative approaches—different configurations, material strategies, or spatial arrangements. Each option should respond to site constraints, planning policy, and the project brief. Cost exercises at this stage provide initial budget validation and help ensure the design ambitions align with financial reality.

The stage concludes with client approval of the architectural concept and confirmation to proceed to Stage 3. The concept should be sufficiently developed that Stage 3 can focus on coordination rather than fundamental design revision. This is a critical decision point—changing direction after this stage wastes consultant time and risks coordination errors.

Stage 3: Spatial Coordination

Stage 02 focuses on the overall project concept with overall plans and volumes, with high level ideas on materiality and aesthetics. In Stage 03, the design begins to zoom into each room, designing each space on elevation. By the end of the stage, the look and feel of the project, internal and external should be clear.

The RIBA Plan of Work states that spatial coordination "is fundamentally about testing and validating the Architectural Concept, to make sure that the architectural and engineering information prepared at Stage 2 is Spatially Coordinated before the detailed information required to manufacture and construct the building is produced at Stage 4."

Guidance continues that "Stage 3 is not about adjusting the Architectural Concept, which should remain substantially unaltered, although detailed design or engineering tasks may require adjustments to make sure that the building is Spatially Coordinated."

What this means is that it is a key stage for integrating primary services and structures into the concept plan layouts. At the end of Stage 03, in theory, consultants should be able to work in relative isolation to produce a tender package. In reality, coordination work always continues into Stage 04, but it is typically looking at much more refined and specific details.

Core tasks include coordinating all architectural and engineering information, completing design studies, and undertaking engineering analysis. Structural beam positions must be resolved with ceiling heights. Service equipment locations should be determined. Building services routes must be coordinated with the structural grid and architectural spaces. The project should fit together in three dimensions.

Planning applications are usually submitted during or at the end of this stage.

While information produced at Stage 3 should be coordinated, it is unlikely to contain sufficient detail for robust contractor tendering. Specifications will be outlined but not complete and this is intentional with Stage 4 allowing adequate time to develop detailed information for manufacturing and construction.

The RIBA guidance recommends implementing change control procedures during Stage 3. Fundamental changes after spatial coordination is achieved generates a great deal of abortive work and use of all consultants time. There are additional coordination risk errors.

By the end of Stage 03 there will be a good sense of the look and feel of a project, with clear references and material palettes.

Drawings will be gaining detail and be fully digital. General arrangement plans, sections and elevations will be at 1:50 scale (as above). Key room elevations, such as bathrooms and kitchens, will be drawn at 1:20 scale to reflect the added detail of design.

Stage 4: Technical Design

Stage 4 produces all design information required to manufacture and construct the project. This includes preparation of technical design in accordance with the design responsibility matrix and construction programme. This is where spatial relationships become buildable details.

For residential extensions, Stage 4 produces construction drawings, specifications, and structural calculations. Building Regulations applications are submitted and tender documentation is prepared. The design is refined to construction tolerance with drawings moving from 1:50 or 1:20 scale in previous stages, to 1:5 detail packages, fully specified for construction. Every detail that a contractor needs to price and build the work should be documented.

As an example of the detail progress through the Stages to this point:

Stage 02 Concept Design

Can suggest a floor is “timber” (this choice would not be confirmed until the next stage, so is deliberately high level).

Stage 03 Spatial Coordination

Adds a simple aesthetic description such as “light natural Oak”

Stage 04 Technical Design

Adds specific descriptions for Contractors to accurately price, such as “15mm engineered natural Oak floorboards (250mm wide planks by minimum length 2000mm) with a 5mm solid wear layer, finished in matt lacquer. 300x300mm sample to be provided by Contractor”.

The stage concludes with the issue of a set of Tender Documents to either a nominated contractor for a Negotiated Tender, or to multiple contractors for a Competitive Tender.

Plans by the end of Stage 04 Technical Design will have sufficient detail for accurate pricing from the Contractor during Tender. Drawings will reference to other details within the overall package and be fully annotated as an accurate description of the works.

A typical call out detail, this showing a new double glazed window in a style to match the historic windows. A mixture of 1:20 scale drawings show the overall window design and layout, while 1:5 details of the window jamb, head and sill clearly describe the construction build-up within the walls and what is visible.

Stage 5: Manufacturing and Construction

Stage 5 comprises the manufacturing and construction of the building, along with associated inspections and resolution of site queries. RIBA guidance states there is no design work in Stage 5 other than responding to site queries. If the preceding stages have been executed properly, construction should proceed smoothly.

The stage name acknowledges the increasing use of off-site manufacturing and modern methods of construction. For residential projects, most of the manufacturing happens on site apart from bespoke joinery, however on larger or complex projects, the boundary between factory and site is shifting.

The architect's role during construction varies depending on the appointment. Under full contract administration, the architect issues instructions, values work, manages variations, and certifies completion. Regular site inspections monitor workmanship quality and compliance with drawings. The architect acts as the client's professional representative throughout the construction process. Often architects perform a Design Monitoring Role, where they become ‘client side’ and act on behalf of the client to review and liaise with the contractor, to review works built for both quality and against the tender documents.

Building Control inspections are coordinated throughout the stage. The contractor must notify Building Control at required stages—foundations, drainage, structural work, fire protection, completion. These inspections ensure the work complies with Building Regulations and protects both client and contractor.

Stage 6: Handover

Stage 6 covers the handover of the building, conclusion of the building contract, and initiation of aftercare tasks. Core tasks include resolving defects, issuing the Practical Completion certificate, and compiling Building Manual documentation.

The practical completion inspection identifies any defects or incomplete works. These must be rectified before practical completion is certified. Once certified, the defects liability period commences—typically 12 months for residential projects. During this period, the contractor remains responsible for defects arising from workmanship or materials.

Building documentation including as-built drawings, operation manuals and maintenance instructions, warranties, and the Health and Safety File will be passed to the client. The Building Regulations Completion Certificate is essential for future property transactions. Without it, selling the property becomes complicated.

Stage 7: Use

Stage 7 covers the building's operational life and feedback into future projects. RIBA emphasises that Stage 7 starts concurrently with Stage 6 and lasts for the life of the building.

Aftercare tasks include seasonal commissioning, performance evaluation, and operational support. The Plan of Work places particular emphasis on monitoring sustainability outcomes—verifying that energy performance, resource efficiency, and other environmental targets are achieved in practice, not just in design calculations.

For residential projects, Stage 7 is usually minimal, with a post-occupancy visit to review how spaces are used and whether design intentions were realised. The key is learning from completed projects—what worked, what didn't, how spaces are actually used—to improve future design quality.

Conclusion

The RIBA Plan of Work provides a coherent framework for organising architectural projects from strategic definition through to long-term use. It reflects contemporary practice, diverse procurement routes, digital coordination and sustainability imperatives.

For practices working on London extensions, the framework offers several benefits. It provides a common language for discussing project progression with clients and consultants. It identifies clear decision points and stage outcomes. It coordinates design development with statutory processes—planning, Building Regulations, CDM compliance. It ensures technical design is sufficiently developed before construction commences.

Most importantly, it is a framework developed through extensive industry feedback and refined over nearly six decades of practice. Used appropriately and adapted to project circumstances, it remains the definitive model for the design and construction process in UK architectural practice.

Read more on the RIBA Plan of Work on the official website, linked below:

https://www.riba.org/work/insights-and-resources/riba-plan-of-work/

For a detailed description of the regulatory environment architects coordinate on behalf of clients, read our Journal post on Building Control, Party Wall and Principle Designer Role:

https://www.armstrongcampbell.co.uk/guide-to-building-control-party-wall-agreements-and-principle-designer-role

Armstrong Campbell Architects is a RIBA Chartered Architect Practice based in East London, specialising in residential extensions, refurbishments and new builds. As a principal-led practice, we offer a personal and bespoke architecture and interior design service.

Residential House Extension Cost in London, 2026 Budget Guide

Sat, 03 Jan 2026 14:17:32 GMT

Residential House Extension Cost in London, 2026 Budget Guide

London extension costs in 2026 for single-storey, two-storey, and loft conversions, plus professional costs and budgeting advice from Armstrong Campbell Architects.

"How much will my extension cost?" is one of the first questions homeowners ask us and one that's hard to answer. Much comes down to the project scope and quality aspirations, which generates a wide range of estimates from £1,500/m² to £4,000/m². This journal aims to provide a detailed breakdown of costs and describe our more nuanced approach to budget estimating.

An example sketch issued to the structural engineer on a recent project that has a tight budget. We can engage early with specialist suppliers and consultants to test cost saving ideas - such as being able to retain as much original structure as possible in this sketch.

Our project cost estimating strategy

We have developed a budgeting strategy for projects that more closely reflects the London construction market and typical projects. This approach separates three types of construction work (new build extension, existing refurbishment, light refurbishment) and gives a sqm rate to apply to each area. The advantage for this is that often clients seek to upgrade entire houses but mainly focus budget thoughts on the extension. Works to the existing house have a major impact on the final budget with sqm rates adding up when accounting for new flooring, plastering, re-wiring or plumbing, as well as general making good and final decorating.

The below figures are what we advise to clients as realistic budget guidelines for residential construction within London in 2025 and into 2026. All costs are approximate based on sqm rates for fully fitted projects (includes bathrooms, kitchens, joinery, lighting etc). The figures do not include VAT, local authority or professional fees.

Benchmark:

Extension: £3000 - £4000 /sqm

(all new floor area added to a project in rear and side extensions or loft spaces).

Existing refurbishment: £2000 - £3000 /sqm

(existing area of house that is being completely renovated with new layouts, services, kitchens or bathrooms).

Light refurbishment: £500 - £1000 /sqm

(existing area of house that is being upgraded, typically the hallways, stairs, front living and bedrooms).

By calculating the floor area of each type of work and multiplying it by the above benchmarks, you can provide an accurate price range for your project. The range will assume simpler volumes, limited bespoke items and simpler finishes at the lower scale, with higher end finishes, integrated joinery and quality systems at the upper end of the range.

An example cost benchmarking during concept design for a ground floor rear extension and loft conversion to a house in Leytonstone, East London.

A real project example Cost Benchmarking

The adjacent page is an example sheet from a cost benchmarking exercise for a House in Leytonstone, London.

The clients are seeking to add a full width rear extension with a living/ dining/ kitchen room that integrates into the existing house footprint adding both a ground floor wc and utility room. The existing living room and corridor spaces will be upgraded.

Using our benchmarking strategy the floor plan was split into three zones and we applied the cost estimate range per zone as follows:

Extension: ~20 sqm = £60,000 - £80,000

Existing refurbishment: ~16 sqm = £32,000 - £48,000

Light refurbishment: ~16 sqm = £8,000 - £16,000

Using estimated areas based on the estate agent plans, the net construction cost ranges from £100,000 - £144,000 .

Conclusion

We will explain additional costs in more detail in the journal below, however the client here wanted higher level finishes and a bespoke extension design. The net construction budget was set at £140,000.

Construction budget - £140,000

VAT (at 20%) - £28,000

Surveys, professional and statutory fees - £25,000

Total budget - £193,000

Budgeting for a project beyond net construction cost

Understandably, clients want to know the "all in" total cost of a project. The previous budgeting exercise is for net construction costs but above this you also have VAT, surveys, professional fees and statutory fees. Additionally, money may need to be set aside if there is requirement for new Furniture, Fixtures & Equipment (FFE) - these are soft furnishings that are typically not part of the Total Sum in the Construction Contract.

As a rule of thumb, clients should allow 20% VAT to be added to net construction cost and anticipate an additional sum of 15-20% for all surveys, professional and statutory fees.

We will run through each additional cost in detailed sections below.

An example plan issued to the contractor on a recent project during concept design stage. The client requested early cost analysis and with the contractor already appointed, we can liaise with them from early stages for high level cost appraisal.

As the project develops and becomes more detailed, architects can begin to engage key suppliers. This drawing was produced to send to a series of bespoke window and joinery manufacturers we have worked with before. It details in enough information the sizing and key relationships of each item, so that we can request initial quotes for the rear façade joinery. These quotes are never fixed until full specifications and tender are released, but it can provide a good estimate of the work and tests market feasibility.

Surveys, Professional Fees and Statutory Fees

D uring the process, you will need to engage and instruct other consultants and specialist surveys. See the list below and some benchmark figures for estimating purposes only (figures all exclude VAT). Please note that the list is not exhaustive and was drafted based on my experience with similar projects in London.

Required Services:

Full Measured Survey

First step is always to get a full measured CAD survey of the house. £1,500 - £2,500.

Drainage Survey

If there are issues with the below-ground drains, it is best to identify these early with a survey. In addition, you may need information regarding manholes as any work affecting a public sewer may require a build-over agreement. £400 - £600.

Structural Engineer

You will need a structural engineer who will provide the necessary structural drawings and calculations for the tender pack, building control, party wall, and construction. Structural Engineers fees will be based on the complexity of project and amount of elements to design - expect 1-2% of construction budget.

Building Control Officer

Typically we recommend using a private firm known as an Approved Inspector. As soon as the detailed drawings are ready they will be issued to the BCO for an initial check, they also visit the site during construction to inspect and approve that the works are being completed according to the regulations. £1500 - £2500.

Read more on Party Wall and Building Control on our journal post:

Guide to Building Control, Party Wall Agreements and Principal Designer Role .

Party Wall Surveyor

You will need a party wall surveyor for any work on a shared wall or garden wall. The basic cost for a notice to be issued is £75 - £100 and these will need to be issued to all the attached freeholders and leaseholders. However, if an award is required, the costs can range between £800 - £1,000 per award.

Planning Applications

For information on full planning applications and permitted development costs, please refer to our detailed post:

Guide to Planning Permission and Permitted Development in London .

Optional Services:

Quantity Surveyor

If desired, for a more accurate understanding of costs early on then we recommend an Initial Cost Plan. £1,000 - £1,500. There is also the option to use a QS for the full service until the end of the project, this would cost £8,000 - £10,000 and may be best suited to higher valued projects.

Landscape Designer

A landscape consultant can re-image your outdoor spaces if you want more substantial changes to the garden, they will also be able to advise on how to preserve or replant. Costs will vary on scope.

Lighting Designer

Architects include fixed lighting specifications for a functional home with typical lighting controls. If there is an ambition for a more bespoke system, a lighting designer would need appointed. Costs will vary on scope.

MEP or AV Consultant

Architects include specifications for a functional home with layouts, coordination and sizing for straightforward servicing proposals. For complex systems, like use of an heat pumps, MVHR, solar panels or audio/ visual, we recommend a specialist M&E or AV consultant. Costs will vary on scope.

Asbestos Survey

If there is suspected asbestos (based on the period of house and any previous works) a survey is required. Allow £500.

Value Added Tax (VAT)

VAT applies to construction costs in the UK, but the rate varies significantly (0%, 5%, or 20%) depending on the type of project, the property's use, a nd whether the builder is VAT-registered. The standard rate of 20% is the default for most work unless specific conditions for a reduced or zero rate are met.

Standard Rate (20%)

The standard rate applies to most construction services and materials, including:

Renovations, maintenance, and repairs of existing residential properties.
Construction of most new commercial buildings (offices, shops, warehouses).
Building extensions or conservatories.
Professional services such as architects' and surveyors' fees.
Hiring goods/equipment.

Reduced Rate (5%)

A reduced rate of 5% may apply to specific residential projects:

Renovating empty homes: For residential properties that have not been lived in for at least two years.
Conversions: Changing the number of dwellings in a building or converting a non-residential building into a home.
Energy-saving materials: Installation of qualifying energy-saving materials like insulation, solar panels, and heat pumps.

Zero Rate (0%)

Zero-rated projects mean no VAT is charged. This typically applies to:

New dwellings: The construction of a qualifying new residential building, provided specific conditions are met.
Charity buildings: Construction of new buildings intended solely for non-business charitable use.
Relevant residential buildings: New buildings used for specific residential institutions like care homes, student halls, or hospices.
Works for disabled people: Certain alterations to a home to suit a disabled person's condition.

For detailed official guidance, refer to HMRC's Buildings and construction VAT Notice 708 .

Cost management throughout a project and role of Architects vs Quantity Surveyor

As a RIBA Chartered Practice and as a registered architect through the governing body Architects Registration Board (ARB), we are bound by two codes of professional conduct. The "RIBA Code of Professional Conduct" ( link here to full document ) states that:

"Members must use reasonable endeavours to advise their

client on the need for specialist advice to assist the client to ascertain and control the cost of the project" .

It is essential to note that while architects assist clients with managing project costs and can advise from a design perspective on how to strategically apportion budget by prioritising value gains, architects are not professional cost consultants - this is the role of Quantity Surveyors.

If throughout the project you wish to get a better understanding of costs we recommend employing a Quantity Surveyor (QS). A QS will provide detailed cost plans at the end of every stage and can provide a Bill of Quantities for the Principle Contractor to price during tender. For larger projects (over £500,000), a QS would be an essential appointment to have a dedicated professional manage your budget in detail.

For projects under £500,000, a full QS service may be considered too expensive. However, for a more accurate understanding of costs early on, you can employ a Quantity Surveyor to produce an Initial Cost Plan after the initial design stages. Allow £1,000 - £1,500 for this.

How do we manage cost at Armstrong Campbell Architects?

We believe in an active collaborative approach to design and construction is required to deliver an efficient project for all parties. We work with clients from our first meeting to establish budgets and project scopes. We have a network of collaborators of other professional services and contractors that can provide early engagement.

Our Stage 04 tender packages include detailed 'Schedule of Works' which are priced by the contactor for a transparent and itemised tender price. This means prior to construction, costs can be aligned. From this point, the best advice that can be given for managing cost is to avoid changes during construction. Late design changes significantly delays contractor's progress on site and therefore can cost more than the same specification or detail, if included prior to tender.

Existing Typical Victorian Terrace House

Side Return Extension

Ground Floor Side Return and Rear Extension

Dormer Roof Conversion

Extension Costs Overview in London (2026)

Single-storey

The single-storey rear extension remains the most popular domestic project in London. A basic specification includes standard brickwork matching existing, double-glazed aluminium windows and doors, flat roof with membrane waterproofing, standard kitchen fit-out as a separate budget, engineered wood flooring, radiator heating, and standard electrical and lighting. A higher specification may include quality facing brick, large format sliding doors spanning 3-4m, large skylights, underfloor heating, flooring such as microcement or solid wood and high-performance insulation materials.

Two-storey

Two-storey extensions cost more per square metre than single-storey work, which surprises some people initially. The reality is that building upwards introduces complexity at every level. The cost premium exists because of more complex structure with first-floor joists and loadbearing requirements, scaffolding required for height access, two sets of windows and doors, plumbing to first floor often for ensuite bathrooms, more complex roof structure, and longer construction time.

Side returns

Side returns reclaim what was often dead space, a narrow passage alongside Victorian and Edwardian terraces that served only to provide space and light between neighbours. They usually cost more per square metre because of fixed costs (scaffolding, skips, fees etc) spread over fewer square metres as well as structural work removing large sections of existing wall.

Loft conversions

Loft conversions offer better value per square metre than ground floor extensions because you're working within the existing footprint with no foundations needed, smaller scale roof alterations, less external work, and shorter construction time of typically 8-12 weeks.

There is still regulatory complexity as loft conversions trigger fire safety requirements that ground floor extensions don't. You need a protected escape route, which often means upgrading your staircase and installing fire doors throughout the house.

Existing joists are often not structurally robust enough to take the load of a new living floor, requiring new structural support. If headroom is generous, a cost effective method can be achieved by retaining existing joists and nestling new floor joists in between, or above. However, typically in Victorian and Edwardian properties the floor to ceiling height is limited in lofts. Given that roof lines are not allowed to be raised due to planning policy, often the required method is to replace the existing floor joists and ceiling to the upper floors.

Additional Considerations for Cost Budgeting

Contingency: 5-10%

Essential buffer for unexpected ground conditions, poor soil, or hidden obstructions, price increases on materials, minor design changes during construction, unforeseen structural issues, and weather delays requiring extended hire. Most projects use 50-80% of contingency and having it in place means these issues become manageable problems rather than project-threatening crises.

Temporary Living Costs

Extensions disrupt daily life more than people anticipate. You can live through a rear extension build, but prepare for dust to penetrate everywhere despite plastic sheeting, for noise starting early and continuing all day, access to garden disappearing, kitchen being unusable for months. Most families cope, but it's tiring and stressful. Allow cost of a temporary kitchen set-up and potentially temporary furniture or fixtures.

If works are extensive, you may need to move out. Should this be the case allow for rental and moving costs. Usually this will be paired with temporary storage facilities for your personal belongings and items such as furniture or curtains that want to remain dust and damage free.

Existing House Works

Extensions don't exist in isolation. Connecting new to old creates interfaces that need resolving. These costs to the existing house can add up quickly and are difficult to avoid if you want the finished result to feel cohesive. Following our above Cost Benchmarking Strategy will ensure appropriate budget is given to existing rooms.

Landscaping Reinstatement

Once you have completed your beautiful new home, you will want a garden that is at least clean and tidy. Gardens are damaged by construction and it is worth budgeting for making good, if not planning a full garden design. Depending on size and scope, it could cost anywhere from £7,500 - £15,000 for a fairly simple reinstated garden. Typical costs to consider:

Paving adjacent to an extension
Turf and planting reinstatement
Boundary walls or fencing
Drainage and soakaways
External lighting

Frequently Asked Questions About Extension Costs

How accurate are online cost calculators?

Not very. They use average costs per m² that don't account for your specific site constraints, specification preferences, property type and age, location within London, or current market conditions. Use them for very rough guidance and feasibility testing before seeking real quotes for your project. Online calculators are useful for initial ballpark figures but dangerous for detailed budgeting. Our Cost Benchmarking Strategy provides a means of adding some nuance to an initial estimate, although it is still only rough guidance.

Should I get multiple quotes for professional fees too?

Yes, but don't choose on price alone. Architects under charging either aren't including full service, with hidden extras later, or are not allowing sufficient working hours to properly execute the project. Architectural fees reflect service scope and expertise, reducing fees usually means reducing service, which creates gaps that cause problems later.

For other professional services we would typically send out invitations to receive three quotes for the package. We find quotes for surveys and building control services are often very closely aligned. In this case, a single quote from a trusted collaborator is sufficient and prioritises speed of appointment. Architects can advise if single quotes fall within a reasonable and expected range.

How much should I budget for a new kitchen?

Kitchen fit-out can cost anywhere from £10,000 - £50,000 depending on size, material quality and fittings. Kitchens are typically the single biggest item spend on projects but are also usually the most-used room in extended homes; compromising excessively here can undermines the overall project.

Budget realistically based on priorities, options include:

High street kitchens from Howdens, Wickes or Ikea provide good variations of designs and are very cost effective.
Traditional designer kitchen companies such as Baumstark or Plain English Kitchens are high quality and have a price tag to match the product.
A number of new kitchen manufacturers such as Reform or Vermland offer interesting materials and detailing in contemporary designs, again at the higher-end scale.
Commonly on DIY projects, Ikea or Howdens base units are paired with bespoke door fronts from Plykea or Naked Kitchens . While there is cost savings in using basic base units, the door fronts from these companies are premium priced and becomes relatively expensive.
Finally, contractors we use have their own joiners or trusted subcontractors that can build bespoke kitchens for surprisingly good value. Plywood is typically used for the base units which is more robust than high street brands chipboard bases. Door fronts can range from a cost efficient spray painted MDF, to mid-ranged timber veneered plywood, or high-end solid timber or metal finishes.

Does Brexit and World Conflicts still affect construction cost?

Material costs have increased significantly since 2019 due to Brexit trade barriers, COVID supply disruptions and increasingly more world conflicts in Europe and the Middle East. These are affecting energy and materials, as well as contributing to general high inflation. Budget based on current pricing and include contingency for any further increases during your project.

Should I wait for costs to come down?

Construction costs have risen above general inflation with timber, steel, and manufactured products having all seen sustained price increases. Typically these rises form the new benchmark and delaying projects is unfortunately more likely to find rising costs.

A concept design visualisation, understanding the full scope of the project - in this case, the client was seeking to test the extent the ground floor rear extension could interact with the garden externally. One proposal was the inclusion of a fixed canopy which blurs the boundary between outside and inside, when paired with a full width sliding minimal door system.

Contact us for Full Architecture Design Services.

Read more of our journal guidance:

Step-by-step guide to RIBA Plan of Work - Guide to RIBA Plan of Work stages →

A detail dive into the design and construction process - Guide To Building Control, Party Wall Agreements and Principle Designer Role. →

Everything you need to know on planning permission - Guide to Planning Permission & Permitted Development in London →

Guide to Building Control, Party Wall Agreements and Principle Designer Role

Thu, 04 Dec 2025 00:00:06 GMT

Party Walls, Building Control and the Principal Designer: A Practical Guide

Armstrong Campbell Architects — East London residential architects specialising in private residential projects and house extensions across London.

Party Wall Agreements

The Party Wall Act 1996 applies across England and Wales to any building work that affects a shared wall, boundary, or nearby foundations. If you're planning an extension or loft conversion in London, it almost certainly applies to you.

When you need to serve notice

Three types of work trigger the Act: building on or astride a boundary, working on an existing party wall (cutting in for beams, raising the wall, removing a chimney breast, structural repairs), and excavating near a neighbouring building — within 3 metres if going deeper than their foundations, or within 6 metres if the excavation cuts a 45-degree line from the foundation bottom.

The process

Notices go out 1–2 months before work starts. There are three types — Party Structure Notice, Line of Junction Notice, and Excavation Notice — and each must include a description of the work, accurate drawings, a proposed start date, and your contact details. In a London terrace, you'll typically be serving both neighbours.

Your neighbour has 14 days to respond. They can consent in writing (work proceeds without an Award), dissent or stay silent (an Award is required), or request changes. Non-response is common in rented properties, so it's worth contacting landlords early so they're ready to respond in time.

If an Award is needed, both parties appoint a surveyor — or agree on a single "Agreed Surveyor," which is more cost-effective and works well when the relationship with your neighbour is good. The surveyors inspect both properties, record their existing condition, and produce a legal document setting out how the work will proceed. This condition schedule matters: if damage occurs during construction, the Award provides a clear record of what was there before.

Surveyors are typically building surveyors or structural engineers with party wall experience. An architect can also act as one, provided they have no conflict of interest — which rules out the project architect.

Costs

If your neighbour consents, the notice itself is free, though having your architect prepare it properly costs around £200–400. An Agreed Surveyor typically runs £800–1,200; two separate surveyors, £1,500–2,500 or more; and if the surveyors themselves can't agree, a third may be brought in at a further £1,000–2,000. For a straightforward London extension with cooperative neighbours, expect to spend £1,000–2,000 total.

Common questions

Can my neighbour stop the work? No. Neighbours cannot prevent work that's permitted under planning or permitted development. The Act facilitates the work safely — it doesn't create a right of veto.

Do we need an Award if we're friends with our neighbours? Yes. Verbal agreements aren't sufficient and leave both parties exposed if something goes wrong later. The formal process protects everyone.

My neighbour says our extension is on their land. Leave this to the surveyor. They'll use their professional knowledge and Land Registry documents to determine where the boundary lies.

The typical London terraced house will have two party walls - a wall shared with a neighbour, highlighted in red above.

Looking in more detail, this plan for a House in Leytonstone shows the party wall condition. This is a boundary line and is the reason why extensions are typically stepped in. Unless agreed with the neighbour, walls have to be built fully on your own land.

Our design will culminate in a detailed drawing package, with the above detail being a typical Party Wall section. This drawing will be reviewed by the Party Wall Surveyor and presented to the neighbour during the award process.

Building Regulations are in place to ensure minimum standards of safety and functionality are embedded within all building work in the UK.

A detailed package will be reviewed by the Approved Inspector, with drawings showing detailed build-ups and annotated specifications clarifying how the design achieves Building Regulation standards.

At Armstrong Campbell Architects, we embed Building Regulation principles from the early concept stage. One recent example was to overcome a common issue of requiring fire separation from the hallway to the kitchen by integrating 30 minute fire rated sliding pocket doors.

Building Control

Planning permission is about how a building looks and its impact on the surrounding area. Building Regulations are about whether it's safe, structurally sound, energy-efficient and accessible. Both matter, and Building Control approval is mandatory for all extensions, loft conversions and significant alterations. Without a Completion Certificate, you'll face problems when selling or remortgaging.

What the regulations cover

The key Parts most relevant to residential extensions are:

Part A (structure and foundations)

Part B (fire safety and escape routes)

Part C (damp and weatherproofing)

Part E (sound insulation)

Part F (ventilation)

Part L (energy efficiency)

Part P (electrical installations)

Part K (protection from falling — stairs, balustrades)

Part M (access)

Local Authority or Approved Inspector?

You have two routes. Local Authority Building Control is run by the council — familiar with local stock, sometimes more flexible in interpretation, but slower to respond and limited to working-hours inspections. Fees typically run £600–1,400 for a standard extension.

Approved Inspectors are private companies offering faster turnaround, dedicated inspectors and more flexible scheduling, sometimes at a slight cost premium — usually £900–1,400 for a similar project.

At Armstrong Campbell Architects, we generally work with Approved Inspectors. The speed of response and ability to pick up the phone to your inspector directly is genuinely useful on a live project. That said, we've worked well with Local Authority too — neither route is inherently better.

Full Plans vs Building Notice

We always recommend a Full Plans application for extensions. You submit complete technical drawings upfront, Building Control reviews them (typically 5–6 weeks for a first review, 2–3 weeks for subsequent responses), and you get written approval before work starts. This prevents costly remedial work later if something turns out to be non-compliant.

Building Notice — where you notify Building Control 48 hours before starting and inspections happen as you go — is better suited to minor interior works.

Construction inspections

Once work begins, Building Control inspects at key stages: foundation excavation (before concrete is poured), damp-proof course installation, oversite preparation, drains (before covering), structural frame, pre-plaster (when insulation, electrics and ventilation are still visible), and final completion. Each inspection needs 48 hours' notice. Missing one can mean opening up finished work — which is expensive.

Common issues to plan for

Energy efficiency (Part L) is increasingly the most demanding aspect of any extension. Current standards require roughly 150–200mm of wall insulation, 250–300mm in roofs, high-performance glazing, and often thermal bridging calculations and airtightness testing.

Structural calculations are mandatory for all extension work — expect to budget £1,500–4,000 for a structural engineer's input, depending on complexity.

Fire safety in loft conversions is non-negotiable and worth understanding early. You'll need a protected staircase with fire-rated doors from loft to ground floor, hard-wired smoke alarms on every floor, a compliant escape window, 30-minute fire-rated floor construction, treated timbers and steels, and fire stopping at all junctions.

The Completion Certificate

After the final inspection, Building Control issues a Completion Certificate confirming the work meets regulations. Keep it with your property deeds. Without it, solicitors will raise enquiries on any future sale — potentially requiring expensive retrospective surveys, or worse, causing a sale to fall through. Indemnity insurance exists for this situation, but it doesn't fix an underlying compliance problem.

The Principal Designer Role

Under the Construction (Design and Management) Regulations 2015, all construction projects with more than one contractor require a Principal Designer. For domestic extensions, this is almost always the architect, sometimes for a small additional fee.

The Principal Designer's job is to manage health and safety during the pre-construction phase — identifying and eliminating foreseeable risks in the design, coordinating information between consultants, and ensuring the Principal Contractor (the builder) has what they need before work starts.

The Principal Contractor then takes over responsibility on site, producing a Construction Phase Plan and providing inductions and welfare facilities for all workers.

At project completion, the client receives a Health and Safety File containing as-built drawings, structural information, material specifications and guidance on safe future maintenance. This should be kept with your property deeds — it's genuinely useful if you ever extend or alter the building again.

Our approach

We identify early whether the Party Wall Act applies, prepare the necessary drawings, recommend surveyors and coordinate timing — notices are typically served b efore planning approval comes through, since the party wall process runs in parallel and needs to be in place before work can start. We guide clients through Building Control from submission to Completion Certificate, and we handle the Principal Designer role as part of our standard service.

Early engagement with all of these — party walls, Building Control, CDM — prevents the kind of last-minute delays that hold up construction starts and add cost.

Armstrong Campbell Architects are a residential architecture practice based in Hackney Wick and Leytonstone, East London, working across London on house extensions, loft conversions, renovations and new builds.

Please contact us to arrange a call or site visit to discuss your project.

Guide to Planning Permission & Permitted Development in London

Wed, 03 Dec 2025 21:46:47 GMT

Guide to Planning Permission & Permitted Development Rights in London

Navigating London's planning system is complex. Between planning permission, permitted development rights, party wall agreements, building regulations, and borough-specific policies, there's a lot to digest before you can start building your extension or loft conversion.

This guide explains everything you need to know—with practical examples from Waltham Forest, Hackney, Brixton and Camden.

At Armstrong Campbell Architects, Leytonstone, we navigate these processes for clients across London. We are experienced in delivering planning applications and understanding what different local authorities require for approval. This guide is intended to share some of that knowledge to assist homeowners project planning.

Our overall strategy is always to be upfront, open and honest - we do not believe in playing games, or overly staged planning applications - these are clear to planning officers and only serve to increase time and cost, as well as unneccessarily congesting the planning system.

Journal post - Learn why working with an architect makes this process easier →

Planning Permission for London Extensions: The Complete Process

Planning permission is your local authority's means of controlling development. It ensures new buildings and extensions respect local character, protect neighbours' amenities and align with Local and National planning policies.

When You Need Planning Permission

You'll need planning permission if your proposed work:

Exceeds permitted development limits (discussed more in this journal post)
Affects a listed building
Is in a conservation area (typically have greatly restricted permitted development)
Involves significant changes to your home's appearance
Could impact neighbours through loss of light, privacy, or outlook
Is on a property with removed Permitted Development rights (Article 4 or planning condition typical on new estates)

Common London projects requiring planning permission:

Two-storey rear extensions
Large single-storey rear extensions
Side extensions on corner plots or narrow sites
Loft conversions with substantial dormers or roof alterations
Front extensions or porches
Basement conversions

The Planning Application Process: Step by Step

Step 1: Pre-Application Advice (Optional)

Before formally submitting, you can request pre-application advice from your local planning department. This typically costs £200-800 with a higher cost if a site visit is requested, the advice can also be given as a 'desktop study' approach. As an example, in Waltham Forest the homeowners advice costs £319 including VAT.

The process involves:

Submitting outline plans and a brief description with existing photos
Meeting with a planning officer (on site or virtual)
Receiving written feedback on likely success and concerns

Is it worth it?

For straightforward planning applications then it is not usually worth the time or cost to pursue advice. In our experience, London councils have reasonably clear planning guidance and strongly rely on precedent projects. Therefore, we always begin our planning research with a Google Earth review and searching the councils recent planning applications for the postcode. Planning outcomes have detailed responses which will state why plans are either accepted or rejected.

For complex projects—conservation areas, contentious designs that go beyond the norm, extra-large extensions—then it would be worth considering pre-application advice. The benefit is to test the water at the same time as progressing the full application package.

Timeline for Pre-Application Advice

This varies between councils, but as an example, Islington commit to arranging visits within 20 days of receiving payment (homeowners will be contacted within 10 days to arrange a date). The visit will last around 30 mins and no definitive advice is given during the meeting. Islington Council commit to giving written advice within 30 working days (6 weeks) of the intial payment date. It is not a quick process and the cost is comparable to a planning application, which is why we only reccomend them if there are specific reasons on a potentially contentious site.

Alternative Pre-Application advice channels

If you would just like a quick call to discuss your project with an expert, Planning Portal now offer 30-minute calls with instant advice and feedback. These cost £72 for homeowners and can be booked online:

https://www.planningportal.co.uk/permission/planning-guidance-service

Step 2: Preparing Your Application

A complete planning application includes:

Drawings (typical scale):

Location plan with site boundary in red (1:2500)
Existing site plan showing boundaries and neighbouring buildings (1:500)
Proposed site plan showing the extension (1:100)
Existing and Proposed floor plans (1:100)
Existing and Proposed elevations (1:100)
Existing and Proposed sections (1:100)

Supporting Documents:

Design and Access Statement (this is text and image based, explaining the proposal)
Heritage Statement (if in conservation area or near listed building)
Fire Risk Assessment's are increasingly more common following the Building Safety Act 2022 update post Grenfell Tower
Other potential reports are Daylight Analysis, Tree Survey, Flood, Transport, Ecological - however these are on a case by case basis

Application fee: Varies by project type:

Householder applications: £528 (as of 2025 the fee's were recently doubled to assist overwhelmed planning departments, although approval times remain at a minimum of 8 weeks)
Prior approval (larger Permitted Development extensions): £240
If your property is Listed, you will need to apply for Listed Building Consent, which is fee free from the council but may incur costs from your planning consultant (if Heritage Statement is required) or architect to prepare the additional documentation.

Step 3: Validation and Consultation

Once submitted, the planning department checks your application is complete (this is called a validation) and usually takes 1-5 working days to be validated. Typical reasons for not getting an application validated includes missing information such as CIL documents, admin errors such as incorrectly named drawings or an unpaid application fee. If the application is not validated, it is not a major issue, you can simply re-submit incorporating the comments, for no additional fee and it is fairly quick, although it pays to triple check the application prior to sending.

Then begins the 8-week consultation period (13 weeks for conservation areas as these are deemed "complex" projects)

Neighbours are notified by letter
A site notice is posted (for conservation areas)
You can track objections and comments online
Planning officer visits the site
Internal consultees (conservation, trees, highways) review

Step 4: Planning Officer Assessment

The planning officer assesses your application against:

National Planning Policy Framework

- https://assets.publishing.service.gov.uk/media/67aafe8f3b41f783cca46251/NPPF_December_2024.pdf

London Plan

- https://www.london.gov.uk/programmes-strategies/planning/london-plan/the-london-plan-2021-table-contents

Local Development Plan

- varies by local authority, available on each website

Planning Application Documents listed above
Previous decisions and local precedent

They'll consider:

Design quality: Does it respect local character?
Neighbour impact: Loss of light, privacy, outlook?
Scale and bulk: Is it proportionate to the existing building?
Heritage: Does it preserve or enhance conservation areas?
Highways: Parking, access, traffic generation
Trees: Impact on protected trees

Step 5: Decision

Planning officers can:

Approve with or without conditions
Refuse with reasons stated
Request revisions informally where you withdraw and resubmit but this is becoming more unusual

Approval rate in London is a round 80-85% for householder applications.

Conditions are common and are usually in place to ensure deveopments are safe, sustainable and fit the area.

Potential types of conditions include:

Construction start date within three years
Material clarifications and potential submital of physical samples
Construction methodology including construction hours
Environmental concerns in case of drainage, landscaping or wildlife
Removal of permitted development rights to prevent future extensions

Key priorities for planning officers when reviewing applications

1. Respect for Local Character

Generic, catalogue designs often get refused in conservation areas. Officers want to see thoughtful responses to context—appropriate materials, roof pitches that match, window proportions that respect the streetscape.

2. No Significant Neighbour Impact

The 45-degree rule is a common test: if your extension projects beyond a 45-degree line drawn from the center of your neighbour's nearest habitable room window, it may cause unacceptable loss of light.

As well as this, extensions on houses with outriggers (the rear volume of house that is typical of London terraces and traditionally has lower ceilings with kitchen and rear bedroom) have restrictions on height of eaves to be no more than 2.5m. This does not include a parapet detail at the front elevation of the extension. This is to protect neighbours light and feeling of enclosure and is why so many London side return extensions have sloped soffits to one side, often with skylights.

3. High-Quality Design and Materials

London boroughs increasingly expect design quality, even for extensions.

Proportionate windows and openings
Appropriate materials
Careful detailing
Thoughtful landscaping and boundary treatments

4. Accurate, Professional Drawings

Professional CAD drawings with accurate dimensions, along with a completness of information within Design and Access Statements show care and confidence on applications. Critically, all information should support the application and all details or dimensions which are considered critical should be clearly annotated (eg 6m extension depths from rear facades as complying with permitted development rights) .

Dealing with Neighbour Objections

Neighbour objections do happen and don't necessarily mean a refusal as planning officers only consider material planning considerations - if a design is within planning policy then it will be approved, otherwise you would have grounds to appeal the decision.

Valid objections:

Loss of light or outlook
Overlooking and loss of privacy
Overbearing scale or bulk
Noise, traffic, or parking impact
Design quality or character concerns

Invalid objections:

Property value reduction
Disputes over boundaries are a civil matter and typically dealt with via party wall agreements

- read our Party Wall Agreement journal post here

Loss of view as this is not a protected right in the UK
Construction disruption - contractors have regulations to work within such as working hours and noise.

How to manage objections:

Engage with neighbours early, ideally before submission to dicuss your plans
Adjust designs if there are legitimate areas of concern that can be accomodated
Write clear Design & Access Statements

Everybody has a right to object on any planning application, the best process is always to keep open dialogue to prevent objections in the first place and avoiding the knowledge black hole and neighbours imagining worst-case scenarios. Fortunately in London, construction of extensions is so common, most neighbours just want to know things will be done well and professionally.

If Your Application is Refused

1. Review the Decision Notice: this will outline the grounds for rejection from the Local Planning Authority

2. Appeal: If you believe the refusal is unreasonable, appeal to the Planning Inspectorate. This takes 12 weeks for householder applications or 6 months for commercial projects. It costs nothing to submit but may incur professional costs. Success rate of appeals is around 30% for householder appeals. It is not a typically a route worth pursuing unless the design is unchangeable.

3. Redesign and resubmit: Usually, the Decision Notice provides clear reasons for rejection. If these can be rectified with an amended design, it is typically most efficient to make the design changes and resubmit a new application. The cost and timeline for the new application will match the original. If the Decision Notice is unclear, you can contact the Planning Officer to discuss their response in more detail.

Permitted Development Rights: Building Without Planning Permission

Permitted Development Rights allow certain home improvements without needing full planning permission. This saves the time waiting on planning applications and also cost less in fees—significant advantages.

What is Permitted Development?

Permitted Development Rights are a set of national rules defining what you can build without planning permission. They cover various home improvements including:

Single-storey rear extensions
Two-storey rear extensions
Loft conversions
Outbuildings
Porches
Solar panels

However, Permitted Development Rights come with strict limitations and important exclusions. It is important to fully understand these prior to starting a project as they cover a range of issues from volumetric, materiality and detailed setting out.

Single-Storey Rear Extensions

This is the most common use of Permitted Development Rights in London.

Standard Permitted Development limits:

Terraced or semi-detached: Up to 3 meters from original rear wall
Detached: Up to 4 meters from original rear wall
Maximum height: 4 meters for pitched roof, 3 meters for any part within 2m of boundary
Eaves height: Maximum 3 meters
Cannot: Extend beyond side walls, use materials significantly different from existing, or take up more than 50% of garden

Larger Permitted Development extensions (with Prior Approval):

Terraced or semi-detached: Up to 6 meters
Detached: Up to 8 meters

For these larger extensions, you need Prior Approval (£240 fee and a 6-week process). Your neighbours can comment and if they object, the local authority will assess the impact on them. If approved or if there is no response after 6 weeks, you can proceed with the works. The recent increase in fee for Prior Approval means that it is sometimes beneficial to do a full planning application which will mean the works are assessed under less strict conditions, while taking only marginally longer to obtain.

Loft Conversions

Loft conversions often fall under Permitted Development Rights in London.

Allowed:

Roof windows on any slope (flush with roof)
Volume increase up to 40m³ (terraced) or 50m³ (detached/semi-detached)
Maximum roof height same as existing
Materials similar to existing

Not allowed:

Dormer windows on front roof pitch (street facing)
Balconies or raised platforms
Increasing overall roof height
Dormers that dominate the roof slope
Dormers that are flush to the facade (300mm set back required)

Important Exclusions from Permitted Development Rights

Where PD does NOT apply:

Flats and maisonettes usually have no rights
Listed buildings will need Listed Building Consent
Conservation areas have many permitted development rights removed
Article 4 Directions is when local authority remove specific rights, usually associated with new housing developments
Properties where rights were removed by previous planning condition

How to check: Contact your local planning department or check online planning constraints maps.

Lawful Development Certificate (LDC)

If you want absolute certainty that your project is permitted development you can apply for a Lawful Development Certificate (£150-400 fee). This provides legal documentation confirming your work doesn't need planning permission.

When to get an LDC:

If you are very close to Permitted Development limits it may be advisable to obtain a LDC. It should be received prior to starting work but can be requested by building control if they require proof works are within limits.

LDC applications take 8 weeks and do not involve neighbour consultation as they are checking against established rights to build.

Frequently Asked Questions

How long does planning permission take in London?

Standard householder applications: 8 weeks.
Conservation areas: 13 weeks.
Prior approval (larger Permitted Development extensions): 6 weeks.

Can I start work while waiting for planning permission?

No - starting work before approval is illegal and can result in enforcement action requiring removal of work at your expense. Wait for the decision notice and ensure conditions are met before beginning any work requiring permission.

What happens if I build without Building Control approval?

It's illegal and creates serious problems:

Local authority can serve enforcement notice requiring exposure of hidden work
Regularisation (backdated approval) costs £1,500-3,000+ and may be refused if defects are found
Lack of building control will create difficulty selling as this is always on solicitors queries, potentially reducing you rproperties ability to sell and subsequent value
No peace of mind that works meet all structural and safety criteria - creating an unsafe environment.

Always obtain Building Control approval.

Do I need both planning permission and building regulations approval?

Often yes, but not always:

Planning only: Some purely appearance changes (windows, doors, cladding)
Building Regulations only: Work under Permitted Development still needs Building Control
Both: Most extensions and loft conversions
Neither: Very minor work (painting, decorating, like-for-like repairs)

Generally, if you're adding space or significantly altering structure, assume you need both.

How much do planning applications cost?

Householder application: £528 (fees were increased in 2025)
Prior Approval: £240
Lawful Development Certificate: £264
Pre-application advice: £200-800

Plus professional fees for drawings and statements.

Can my neighbours stop my extension?

No - they can object to your planning application but planning officers make decisions based on planning policy and not on neighbour preference. However, well-founded objections on valid planning grounds can influence decisions. Similarly, under the Party Wall Act, neighbours cannot veto any work but must allow works to proceed under correct process. Legislation is there to faciliate construction rather to stop it.

What if my extension fails Building Control inspection?

The inspector will note the failure and explain what's needed to pass. Your contractor can make corrections and then requests a re-inspection. Failures cause delays but are should be resolvable. This is why Building Control exists—catching problems before they're hidden or create long-term issues. Following good guidance with detailed submission packages and regular site visits, where the ongoing works are clearly displayed, should mitigate well against unforeseen rejection.

How long does Building Control approval take?

Full Plans approval takes 5-8 weeks typically. Once approved, inspections happen as the work progresses on site. This is usually within 1-2 days of a request to attend by the contractor. The Completion Certificate is issued 1-2 weeks after final inspection and signals Building Control is successfully obtained.

Contact us for Full Architecture Design Services, Planning Applications or to book a Home Design Consultation .

Read more of our journal guidance:

What to expect from working with an architect - Do I Need an Architect For A London Extension Or Loft Conversation? →

A detail dive into the design and construction process - Guide To Building Control, Party Wall Agreements and Principle Designer Role. →

armstrong campbell architects

Based in Leytonstone, London
Residential and Hospitality Architects

House Extension | Loft Conversions | Renovations | New Builds

Last updated: December 2025